Admiral Barrie said if authorities try to board and redirect a boat found in international waters, that could break international piracy law.

Mr Ruddock said the Howard government received extensive legal advice before deciding to turn asylum seeker boats back to Indonesia.

He said the Coalition enacted the policy in a way that ensured it was not an issue.

"We took comprehensive legal advice from the international area of the Attorney-General's Department as to the manner in which our forces should engage with those seeking to access Australia without lawful authority," he said.

Mr Ruddock said Labor policies had not worked and the recent surge in arrivals would make the issue more challenging.

"What we are dealing with is a situation very much more difficult because of the numbers involved and the expectations," he said.

"You won't deal with those matters unless you use all the weapons in your armoury."

'Unprecedented flow of boats'

More than 4,000 asylum seekers have arrived on the island since January.

Christmas Island's administrator, Jon Stanhope, said the number of recent arrivals was unusual.

"There certainly has been, over the last month, an unprecedented flow of boats, probably averaging about one a day," Mr Stanhope said.

Mr Stanhope said chartered planes were regularly used to transfer the asylum seekers off the island.

He said locals accepted the regular arrivals with good grace, but they held concerns about local infrastructure.

"There is a concern within the community that some of the infrastructure needs that go to the quality of life of permanent residents do need to be given perhaps as much attention or at least equal attention by the Department of Immigration," he said.

Mr Stanhope said he was not concerned about potential unrest within the detention centres.